The present invention concerns a support beam for at least one oblong tool, for instance for a scraper blade or for two scraper blades.
A support beam of a type to which the present invention is directed is a so-called scraper beam. It forms together with the scraper blade(s) a so-called scraper intended for use in a machine for the production or processing of fibrous webs, for instance paper webs. The scraper blade can interact, e.g., directly with the shell surface of a rotating roll or of a drying cylinder in order to keep the shell surface clean or to pick the paper web off the shell surface. In paper coaters, the scraper bar makes direct contact with the paper web in order to remove surplus coating mixture.
U.S. Pat. No. 3,134,126 describes the problem that the major part of the scraper beam, i.e., the primarily box-shaped oblong hollow body, may sometimes flex, so that the scraper bar will (across its length) not be forced on the roll with a uniform line force. This flexure is caused in that one of the length walls of the hollow body assumes during operation a temperature higher than that of another length wall. To solve this problem, channels are provided inside the hollow body of the prior scraper beam. A tempering fluid flows through the channels. The objective is keeping the hollow body isothermal, thus avoiding the mentioned flexure. This prior design requires a high construction expense and complex control systems intended to safeguard the desired success.
U.S. Pat. No. 3,800,357 describes the same problem. As a solution to the problem, it provides for the following, based on a cross section of the scraper beam. An elastic support arm supports, on the one end, the scraper blade while, with its other end, it is mounted on the scraper beam. The latter has a drop type cross-sectional shape, i.e., it is a welded structure of two length walls with a convex curvature, their radius of curvature being greater than their width. Formed along one of the welds is an acutely angled edge extending at a relatively small distance from the scraper blade. This accomplishes that the scraper blade--less so than with a conventional beam design--participates in a thermally caused flexure of the beam. However, a completely uniform line force is still not achieved between scraper blade and roll, since the cause (namely the thermal beam flexure) has not been eliminated.
German utility patent application G 91 13 542.7 proposes to fabricate the oblong hollow body of the scraper beam of a fiber composite material in which the coefficient of thermal expansion resides in the so-called major fiber orientation near the value of zero and where the major fiber orientation extends approximately parallel to the longitudinal axis of the scraper beam. The hollow body favorably is to be made of a plastic reinforced with carbon fibers. Due to these measures, the hollow body can be kept free of flexure in a way simpler than according to U.S. Pat. No. 3,134,126, even if its length walls assume in the operation different temperatures. At the same time, as compared to steel, a lower weight is achieved in known fashion, along with a relatively high rigidity, i.e., reduced deadweight flexure at same dimensions.
Problematic of German patent application G 91 13 542.7, however, is the conventional design of the hollow body length walls as flat walls. Due to the major fiber orientation in the longitudinal direction, the rigidity of the hollow body is relatively low in peripheral direction. Hence, the safety against vibrations (the so-called panel vibration) and/or denting is insufficient with the flat length walls. Besides, the flat length walls are jeopardized by mechanical shock loads, for instance in the shipping or assembly of the scraper beam.
Underlying the present invention, therefore, is the problem of designing quite generally a support beam whose major part (the said hollow body) is to be made of a composite fiber material in such a way that the longitudinal walls of the hollow body--despite the major fiber orientation extending for the most parallel to its longitudinal axis--are sufficiently rigid, so that especially a sufficient denting safety will be given. Another part of the problem definition is that the known, extensively box type shape of the support beam (e.g., with a mostly triangular cross section) is to be retained to the maximum extent, due to its known high flexural and torsional strength.